Return to Marine Biololgy
Chapter 6
Invertebrates

Sponges / Poriferans

• They have tiny pores instead of mouths
• Most of their cells line a series of connected chambers and channels
• They are composed of collar cells, pore cells, and wandering cells which can easily change type
• Water is drawn into the pores and out the top of the sponge by flagella
• Collar cells filter food from the water as it passes by.
• Cells function independently and perform a variety of functions.
• Spicules and spongin are use for support

http://www.ucmp.berkeley.edu/porifera/porifera.html

Cnidarians/Anemones, Jellyfish, Corals

• Grouped together because many of the species have a particular type of sting-cell
• Most have a polyp or sack like stage and a medusa or bell shaped stage.
• They have not head, no skeleton, and no special organs for respiration or excretion
• They have:
• Nematocysts – stinging-cells that eject barbed threads tipped with poison
• Radial symmetry, where similar body parts encircle a central axis
• Mouths surround by tenticles
• Mouth sides (oral surfaces) and sides away from the mouth (aboral surfaces)
• Blind gut cavities
• Body walls with two layers of cells
• Nerve-nets – interconnected neurons lacking a brain http://faculty.washington.edu/chudler/invert.html

http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html

Three Common Groups of Cnidarians:
Hydrozoans

• Are the most diverse group
• Some form feathery or bushy colonies
• Some form drifting colonies
• Some have specialized floats
• Unlike true jellyfish they are composed of colonies of individuals, all specialized for various functions
• Examples: hydra, fire corals, and the "Portuguese man-o'war."

http://www.ucmp.berkeley.edu/cnidaria/hydrozoa.html
Scyphozoans

• The larger, true, jellyfish
• The medusa is the dominant stage in most
• Swim with rhythmic contractions

http://www.ucmp.berkeley.edu/cnidaria/scyphozoa.html
Anthozoans

• Most lack a medusa stage
• They exist as solitary or colonial polyps (corals)
• Some have large muscular polyps (anemones)
• Some have calcium carbonate skeletons (corals)
• Some have branching protein skeletons (Sea fans and black corals)
• Some form fleshy colonies (Soft corals, sea pens, and sea pansies)

http://www.ucmp.berkeley.edu/cnidaria/anthozoa.html

Flat Worms / Platyhelminthes

• Simplest animals with three cell layers
• bilaterally symmetrical – could be cut into two similar halves
• Has a gut, but no anus (Food and wastes move through the same opening)
• Gut may be branched, so it is close to more cells
• Respires by diffusion, so a flat shape keeps a surface close to more cells
• Brain is just a small group of nerve cells in the head

Trematoda, or flukes, are all parasitic (live in lungs and liver tissue)
The Cestoda, or tapeworms, are intestinal parasites in vertebrates
http://www.ucmp.berkeley.edu/platyhelminthes/platyhelminthes.html
http://www.biocrawler.com/encyclopedia/Flatworm__

Ribbon Worms / Nemerteans

• Gut includes a mouth and anus
• Blood transports nutrients and oxygen to tissues
• Proboscis – long fleshy tube to entangle prey
• Longest animal on earth

http://www.ucmp.berkeley.edu/nemertini/nemertini.html
http://www.biocrawler.com/encyclopedia/Nemertea

Roundworms / Nematodes
Live in sediments or are parasites
They have:

• Cylindrical bodies with points on both ends
• A mouth and anus
• A gut that lies in a fluid filled body that transports nutrients
• A hydrostatic skeleton made by layer of muscle that pushes and squeezes the fluid filled body aiding movement

http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html
http://www.biocrawler.com/encyclopedia/Roundworms

Segmented Worms / Annelids
They have:

• A body consisting of a series of similar compartments
• A guts that lies in a cavity called a coelom that passes all segments
• A fluid filled coelom that a long with muscles in the body wall form a hydrostatic skeleton
• A closed circulatory system with contractions in vessels moving blood

Some have extensions of the body wall that absorb oxygen – gills
Some have specializations to suck blood
http://www.ucmp.berkeley.edu/annelida/annelida.html
http://www.biocrawler.com/encyclopedia/Annelid


Lophophorates
Three groups of marine invertebrates

• Bilateral filter feeders with a U-shaped gut
• They have a unique feed structure called a lophophore.
• Lophophore are a circular or coiled arrangement of ciliated tentacles.

Bryozoans – moss animals
http://www.sms.si.edu/IRLSpec/IntroBryozoa.htm
http://www.ucmp.berkeley.edu/bryozoa/bryozoamm.html
http://www.tolweb.org/Bryozoa
http://www.ucmp.berkeley.edu/bryozoa/bryozoa.html

Phoronids – worm-like and build tubes partially made of sand
http://www.ucmp.berkeley.edu/brachiopoda/phoronida.html
http://www.solaster-mb.org/mb/phoronida.htm

Brachiopods – have a top and bottom shell, but are very different from clams
Many are found in the fossil record.
http://en.wikipedia.org/wiki/Brachiopod
http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html

Mollusks / Snails, sea slugs, clams, octopuses, and chitons
Features common to some species:

• Shell secreted by a thin tissue layer
• Muscular ventral foot
• Head with eyes
• Radula – a rasping tongue
• Gills
• Salivary and digestive glands
• Both closed and open circulatory system

Gastropods
Snails, nudibranchs and sea hares
http://en.wikipedia.org/wiki/Nudibranch

Bivalves
http://en.wikipedia.org/wiki/Bivalves
http://www.solaster-mb.org/mb/bivalvia.htm

Cephalopods
http://www.tolweb.org/Cephalopoda
http://en.wikipedia.org/wiki/Cephalopod

Crustaceans

General characteristics:

• Segmented bodies
• Jointed legs
• Chitinous exoskeleton

Special share characteristics of some:

• Two pairs of antenna
• Mandibles for chewing
• A pair of appendages on each body segment
• Teardrop-shaped larvae
• Molting
• Compound eyes
• Small simple brains

Barnacles/ Class Cirripedia

• Begin as free-swimming larvae
• Cements its back to a suitable surface
• Catches or filters food with its feet
• Forms a calcium carbonate shell
• Hermaphrodite

Copepods

• Abundant in plankton and a major food for plankton feeders
• Filter or capture food with mouthparts
• Swim with antenna

Decapods and Krill__ / Malacostraca
Includes lobsters, crab, and shrimp
Characteristics:

• Ten legs
• Claws
• Carapace that encloses the gills

The large nets used to catch shrimp often kill many other kinds of animals